The Account ID should be configurable with the Text Field for the fixed prefix and a dynamic value option with the characters limit option, so that if the user wants to identify the Account based on a certain text field, they can do so with the help of the initials of the word(s). There can be some of the Account ID formats for the quick identification of the Account, based on the name, Industry type, Country, Region, etc.
Also, the auto numbering should be available from 100 onwards, with the option to select the length of number and resettable as and when required by the admin.